JP2006037088A - Water-based ink and ink set for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ink which contains a self-dispersing colorant, forms images having enhanced scratch resistance and marker resistance, realizes the achievement of good image grades and color development, achieves image stability, and can prevent inks having different hues from blotting between the images of the inks. <P>SOLUTION: The water-based ink comprising a coloring material and water is characterized in that the coloring material is a dispersible colorant comprising a colorant and chargeable resin pseudo fine particles smaller in size than the colorant, wherein the chargeable resin pseudo fine particles are fixed to the colorant, and the ink further contains at least one kind of salt selected from the group consisting of (M1)<SB>2</SB>SO<SB>4</SB>, CH<SB>3</SB>COO(M1), Ph-COO(M1), (M1)NO<SB>3</SB>, (M1)Cl, (M1)Br, (M1)I, (M1)<SB>2</SB>SO<SB>3</SB>, and (M1)CO<SB>3</SB>, (M1 represents an alkali metal, ammonia, or an organic ammonium; Ph represents a phenyl group). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a water-based ink containing at least a dispersible colorant suitable for ink jet recording and a salt, and an ink set for ink jet recording using such an aqueous ink.

  Conventionally, as coloring materials used in water-based inks, there are mainly dyes and pigments. Conventionally, water-soluble dyes have been mainly used due to their ease of handling as water-based inks and high color development properties. As a coloring material for water-based inkjet recording ink that can realize high weather resistance and water resistance of an image, development of a coloring material that is essentially insoluble in water, particularly an ink using a pigment, has been energetically advanced.

  In order to use a color material insoluble in water, particularly a pigment, as an aqueous inkjet recording ink, it is necessary to stably disperse the color material in water. In this case, generally, a method of stabilizing the dispersion using a surfactant or a polymer dispersant (hereinafter also referred to as a dispersion resin) has been used. However, when the pigment is stabilized and dispersed using the dispersant as described above, particularly when recording is performed on a recording medium in which ink such as plain paper easily penetrates, the ink penetrates into the inside of the recording paper, In some cases, the cellulose on the surface of the recording paper is exposed or the ink oozes along the fibers of the cellulose, resulting in deterioration of character quality or color developability.

  In order to solve such a problem, a method of chemically modifying the surface of the water-insoluble colorant has been proposed (for example, see Patent Document 1). Such a water-insoluble colorant is usually called a self-dispersing pigment, and the dispersion stability of the pigment is achieved not by a dispersant but by an electrostatic repulsive force of a modified functional group. When this pigment is applied to the recording paper, the dispersion becomes suddenly unstable due to pH change or evaporation of moisture, so that the penetration and bleeding of the ink into the recording paper can be suppressed, and the water-based ink using the above-described dispersant has The problem can be solved. In addition, the water-based ink containing such a pigment does not require the use of a dispersant such as a polymer dispersant, and thus has the characteristics that the viscosity of the ink can be kept low and the moisture is quickly dried. ing.

  The characteristics of the ink as described above are suitably used in water-based ink for ink jet recording. For example, a salt is added to a water-based ink containing a water-insoluble colorant that does not use a dispersant, so that dispersion destruction is instantaneously performed on the recording paper, thereby obtaining a high density and suppressing ink bleeding. A black ink for water-based inkjet recording that realizes printing quality has been proposed (see, for example, Patent Document 2).

  However, in the case of an ink configuration in which a dispersant such as a polymer dispersant is not used and a water-insoluble color material is localized on the surface of the recording paper, the color material is present in the vicinity of the recording paper surface and the resin is Therefore, there is a problem that the scratch resistance and marker resistance of the recorded image tend to be lowered. On the other hand, in order to improve the scratch resistance of the image, it is conceivable to add to the ink a polymer compound that functions as a binder for the color material. In this case, however, the addition of a polymer compound that functions as a binder for a water-insoluble colorant, particularly when the ink composition is designed to improve character quality by adding salt as described above. Has a salting-out effect by salt, and remarkably deteriorates its storage stability.

  On the other hand, chemical modification treatment for water-insoluble colorants has been often applied to carbon black. This is because the change in color tone caused by the chemical modification treatment is hardly a problem when the color tone is black. On the other hand, in the case of organic pigments such as yellow, magenta, and cyan, if the degree of chemical modification of the pigment surface is increased for the purpose of enhancing dispersion stability, the color tone becomes dark and a clear full-color image is obtained. Sometimes it could not be realized.

  As described above, in the case of a water-based ink using a self-dispersing pigment that does not use a dispersant, the formed image realizes good character quality and color developability, such as scratch resistance and marker resistance. Problems with image robustness were likely to occur. In the case of water-based inks that use a combination of the above-mentioned self-dispersing pigment and salt, it is possible to further improve the character quality and color developability of the formed image, but image fastness such as scratch resistance and marker resistance is It was in the direction of decline. Further, when the good image quality achieved by the self-dispersing pigment is applied to other than black, there is a problem that the color tone of the color pigment becomes turbid and image sharpness is remarkably lowered.

Japanese Patent Laid-Open No. 10-195360 JP 2000-198955 A

  The object of the present invention is to improve the scratch resistance and marker resistance of the formed image in the water-based ink using the self-dispersing color material, thereby achieving good image quality and color development and at the same time being excellent. To achieve image robustness. In addition, the object of the present invention is to solve the above-mentioned problems of the prior art, have a sufficiently high dispersion stability suitable as a coloring material for ink jet recording ink, and there is no detachment of the resin component from the coloring material. Another object of the present invention is to provide a water-based ink suitable for ink jet recording, which can obtain a high-quality image excellent in image fastness by using an excellent dispersible colorant that is stable over a long period of time. Another object of the present invention is to generate bleeding (bleed) in a boundary region between different color tones when an aqueous ink containing a self-dispersing color material is applied to an ink set having two or more different color tones. This is to realize a small number of recorded images (hereinafter, such ink characteristics are referred to as “bleed characteristics”).

  As a result of intensive studies on the means for solving the above problems, the present inventors have achieved a high dispersion stability essentially without using a surfactant or a polymer dispersant by using a dispersible colorant having a novel form. The development of a new dispersible colorant that has long-term storage stability without losing the resin component from the colorant. And by using such a dispersible color material and a specific salt in addition to this, it has sufficient ejection stability and dispersion stability for inkjet recording applications, and further has high image quality and scratch resistance. It has been found that a water-based ink which can give a printed matter having excellent image stability such as marker resistance and which is particularly suitable for ink jet recording can be obtained. That is, the object of the present invention is achieved by the following specific means.

The present invention relates to a water-based ink containing a colorant and water, wherein the colorant has a color material and chargeable resin pseudo fine particles smaller than the color material, and the color material, the chargeable resin pseudo fine particles, In the ink, and (M1) ₂ SO ₄ , CH ₃ COO (M1), Ph-COO (M1), (M1) NO ₃ , (M1) Cl, (M1) Br, (M1) I, (M1) 2 SO 3 and (M1) CO ₃ (where, M1 denotes any one of an alkali metal, ammonium or organic ammonium, Ph represents a phenyl group.) An aqueous ink containing at least one salt selected from the group consisting of:

  Another embodiment of the present invention is an ink jet recording ink set in which at least one kind of ink is the above-mentioned water-based ink in an ink jet recording ink set having two or more inks.

  According to the present invention, a water-based ink capable of obtaining a high-quality character with little ink bleeding, an image characteristic and an image having high color developability, and an image excellent in image fastness such as scratch resistance and marker resistance. (Hereinafter referred to as ink). In addition, according to the present invention, by applying the above excellent ink to any one of inks constituting two or more different color tone ink sets, an image having high color developability with little intercolor bleeding (bleed). An ink set capable of recording is provided. Such an effect is achieved by using a dispersible color material in which chargeable resin pseudo fine particles smaller than the color material are fixed on the surface of the water-insoluble color material. That is, the dispersible colorant has a resin component on the colorant surface and does not desorb the resin component from the colorant, so that the water-insoluble colorant is sufficiently dispersed at the high functional group density of the resin. Can be stabilized. Further, an image formed using the ink by the resin constituting the fine particles becomes an image excellent in image fastness such as scratch resistance and marker resistance. In addition, since the ink according to the present invention contains a specific salt in addition to the dispersible colorant, the salt is instantaneously dispersed and broken on the recording paper by the salt, and the ink is applied to the recording paper. As a result of suppressing penetration and bleeding, it is possible to realize image recording with high color developability with little intercolor bleeding (bleed).

  In addition, according to the present invention, the above-described excellent dispersible colorant is used as a component of the ink and a specific salt is used, so that sufficient ejection stability and dispersion stability can be achieved for inkjet recording applications. Excellent water-based ink that gives a printed matter with high image quality and excellent image fastness, and using this, in particular, realizes high-coloring image recording with less bleeding between different colors (bleed) An ink set is provided.

  Hereinafter, the present invention will be described in detail with reference to an embodiment which is considered to be the best of the present invention. As used herein and in the claims, the meaning of “dispersible colorant” is essentially dispersible in water or aqueous ink media without the addition of surfactants or polymeric dispersants. That is, it is a color material having self-dispersibility.

  First, the dispersible color material used in the ink according to the present invention is a dispersible color material having a color material and chargeable resin pseudo fine particles smaller than the color material, wherein the color material and the charge material are charged. The adhesive resin pseudo fine particles are fixed. In particular, the color material is preferably one in which a plurality of the chargeable resin pseudo fine particles are scattered and fixed to the color material. The dispersible colorant used in the present invention will be described later.

The ink according to the present invention is characterized in that the dispersible colorant is used and contains the following salts in combination with the colorant. That is, the salts used in the present invention are (M1) ₂ SO ₄ , CH ₃ COO (M1), Ph-COO (M1), (M1) NO ₃ , (M1) Cl, (M1) Br, (M1) I. , (M1) ₂ SO ₃ and (M1) CO ₃ , wherein M1 represents an alkali metal, ammonia or organic ammonium, and Ph represents a phenyl group.

  Specifically, Li, Na, K, Rb, Cs, or the like can be applied as the alkali metal. Examples of the organic ammonium include methyl ammonium, dimethyl ammonium, trimethyl ammonium, ethyl ammonium, diethyl ammonium, triethyl ammonium, trimethanol ammonium, dimethanol ammonium, ethanol ammonium, and triethanol ammonium. Salts that can be most suitably applied in the present invention include ammonium benzoate, ammonium phthalate, ammonium sulfate, ammonium acetate, ammonium nitrate, ammonium oxalate, and ammonium citrate. These salts are ionized in the ink. For example, ammonium benzoate is ionized into a cation component of ammonium and an anion component of the carboxyl ion of benzoic acid.

  When the amount of these salts added to the ink is increased, the ink bleeding is suppressed and the color developability is improved, but the dispersion stability and storage stability of the water-based ink tend to deteriorate. Therefore, it is preferable to add the largest amount within the range in which necessary storage stability can be realized from the viewpoint of product specifications. From this point of view, it is preferable to contain 0.05 to 5% by mass of salt in the proportion of the water-based ink.

  Further, as the color material constituting the dispersible color material, a water-insoluble color material having a hydrophilic surface on the color material is preferable. That is, the dispersible color material used in the present invention is configured by fixing the chargeable resin fine particles to the surface of the color material such as a pigment, but the color material surface to which the resin fine particles are not fixed is described below. For reasons, it is preferably hydrophilic. A general coloring material such as carbon black has a hydrophobic pigment surface, and adsorbs a dispersing agent such as a polymer dispersing agent or a surfactant, thereby stabilizing the dispersion. For this reason, when these surfactants are used in the production process of the dispersible color material used in the present invention or the ink formulation, the color material surface, which is the main feature of the ink according to the present invention The coloring material is stably dispersed in the aqueous medium by the electrostatic repulsive force of the chargeable resin fine particles fixed to the ink. On the other hand, due to the action of a specific salt contained in the ink, the ink is transferred onto the recording paper. When it is applied to the structure, there is a possibility that the configuration that instantaneously causes dispersion destruction may be hindered. That is, in this case, on the contrary, the occurrence of bleeding and the color developability may be deteriorated.

  Here, the degree of hydrophilicity of the pigment surface varies depending on the degree of oxidation of the surface oxidation, and according to the study by the present inventors, the character quality and color developability may also vary depending on the degree of oxidation of the color material used. all right. That is, the higher the degree of oxidation of the color material surface, the weaker the adsorption of the dispersant, and as a result, the printing characteristics of the resulting ink are improved.

  In the case of a general organic pigment, the degree of hydrophilicity of the surface varies depending on the polarity of the constituent molecules of the pigment. In particular, the hydrophilicity of the surface of a pigment having oxygen or a hydroxyl group in the pigment molecular structure is high. Further, the surface hydrophilicity varies depending on the processing method of the finishing process performed at the end of the pigment manufacturing process. For example, when the pigment is subjected to a drying process after being replaced with an aqueous solvent, or when finishing with an aqueous solvent containing an aqueous resin or the like, the surface hydrophilicity of the pigment increases.

  As described above, in particular, carbon black generally has a hydrophobic surface and easily absorbs the dispersant, so that bleeding is likely to occur. In particular, carbon black produced by the furnace method has few hydrophilic groups such as carboxyl groups and hydroxyl groups on the pigment surface, and its surface is hydrophobic. In order to make the surface of such carbon black hydrophilic, it is preferable to impart a hydroxyl group or a marine group by oxidation treatment. On the other hand, even with the same carbon black, gas black such as Degussa manufactured in an environment where oxygen is relatively present has a hydrophilic group on the surface and has a characteristic that it is difficult to adsorb a surfactant. Is. Examples of such gas black include FW1, FW2, and FW200 manufactured by Degussa.

  The degree of hydrophilicity (oxidation) of the carbon black surface is evaluated as the volatile content (%) of carbon black. Normally, when carbon black is heated to about 1,000 ° C. under vacuum, a gas corresponding to the type of functional group present on the surface is generated, and the total amount of the gas or the gas species is analyzed. The type and amount of surface functional groups can be known. Moreover, it turns out that it is carbon which has a large amount of hydrophilic groups, so that the sum total of heating weight reduction amount is high.

  There is almost no hydrophilic group such as a carboxyl group or a hydroxyl group on the pigment surface, and the volatile content of hydrophobic carbon black by the ordinary furnace method is 2% by mass or less. Moreover, carbon (for example, BP-L manufactured by Cabot Corporation in the United States) generally marketed as hydrophilic carbon has a volatile content of about 5% by mass. Even if the dry oxidation treatment is sufficiently performed on the carbon black, the volatile content is 10% by mass or less.

  On the other hand, a wet oxidation method is mentioned as a method which can raise the oxidation degree of the surface of carbon black more. In this method, carbon black is impregnated in the aqueous phase, an oxidizing agent such as peroxodiacid or peroxodiacid salt is added, and the reaction is performed at about 60 to 90 ° C. to perform surface oxidation. More specifically, such wet oxidation on carbon black can be carried out by the method described in JP-A-2003-183539. As another wet oxidation method, there is a method of oxidizing using hypochlorous acid such as sodium hypochlorite and potassium hypochlorite as described in JP-A-2003-96372. At this time, as the carbon to be oxidized, a more uniform oxidation is possible when a relatively hydrophilic carbon such as gas black or acidic black is used. Furthermore, as described in Japanese Patent No. 3510897, it is also possible to add a carboxyphenyl group or a sulfophenyl group directly to carbon using an aromatic diazonium salt in a broad sense. Can be defined.

  In this way, if the surface of the pigment, which is hydrophobic carbon black, is made hydrophilic, if the adsorption of the polymer dispersant or surfactant is suppressed, the dispersion stability of the pigment due to the adsorption of the surfactant decreases. As a result, it is better to instantly aggregate the color material on the recording paper by allowing the ink to contain salt. On the other hand, the dispersion stability of the pigment and the fastness of the image formed by using it in the ink are compared with the conventional self-dispersion pigment by fixing the chargeable resin pseudo fine particles used in the present invention to the pigment. It is possible to greatly improve.

  The first characteristic of the dispersible color material used in the present invention is a dispersible color material comprising a color material and a chargeable resin pseudo fine particle, and the color material fixes the chargeable resin pseudo fine particle. There is in point. FIG. 1 is a schematic diagram of a dispersible color material, which characterizes the present invention, in which chargeable resin pseudo fine particles 2 are fixed to a color material 1. A portion 2 ′ in FIG. 1B is a portion schematically showing a state in which a part of the chargeable resin pseudo fine particles 2 fixed to the surface of the color material 1 is fused.

  By fixing the chargeable resin pseudo fine particles to the color material, the charge of the chargeable resin pseudo fine particles is imparted to the surface of the color material, so that the dispersible color material can be dispersed in water or an aqueous ink medium. At the same time, the dispersible colorant has excellent adhesion to the recording medium due to the presence of the resin component adhering to the surface. At this time, since the chargeable resin pseudo fine particles, which are the characteristic of the dispersible color material used in the present invention, are not in a simple physical adsorption of the resin component, the charge resin pseudo fine particles are fixed to the color material. Since it does not detach from the color material surface, the dispersible color material used in the present invention is excellent in long-term storage stability.

  Here, the chargeable resin pseudo fine particles in the present invention are resin aggregates in which the resin component is strongly aggregated, and preferably have many physical crosslinks formed therein (resin aggregates and Is a resin component having a stable form as a fine particle form or a microaggregate close to it). Details of the chargeable resin pseudo fine particles will be described later.

  The state where the chargeable resin pseudo fine particles are fixed to the color material in the present invention is due to the strong interaction between the color material surface and the chargeable resin pseudo fine particles, and is considered to be achieved in the following state. FIG. 4 shows a schematic diagram in which the interface of the chargeable resin pseudo fine particles in contact with the color material is enlarged. First, the chargeable resin pseudo fine particles 2 are formed by intertwining polymers composed of various monomer unit compositions (indicated by 9-1 and 9-2 in the figure). Since the polymer has various structures locally at the interface with the colorant, various states are distributed in the local surface energy. The color material and the polymer are strongly bonded in that the surface energy generated from the chemical structure and the surface structure of the color material and the surface energy generated from the chemical structure and the surface structure of the polymer are well matched locally. (The part indicated by a black circle in the figure). Furthermore, as shown in FIG. 4, there are a plurality of points where the surface energies of both are locally coincident with each other at the interface where one chargeable resin pseudo fine particle is in contact with the coloring material. It is expected that the fixed state of the present application is established by the strong interaction at the plurality of locations. In the present invention, a state in which, for example, 30% or more of the surface area of the chargeable pseudo fine particles, such as 2 ′ in FIG. 1B, is in contact with the coloring material is referred to as “fusion” for convenience. Is a form of fixation, and there is no need for the chargeable pseudo fine particles and the color material to melt together at the interface.

  In particular, a strong interaction is exerted between constituent polymers inside the chargeable resin pseudo fine particles, and in some cases, the constituent polymers are entangled with each other to form a physical crosslink. For this reason, even when the chargeable resin pseudo fine particles have many hydrophilic groups, the fixed charge resin pseudo fine particles are detached from the coloring material or have hydrophilic groups from the chargeable resin pseudo fine particles. The resin component does not continue to elute. On the other hand, in the encapsulation method as described in Patent Document 2, since the highly hydrophilic resin cannot be strongly bonded to the coloring material, the resin is detached from the coloring material, and as a result, the long-term storage stability is sufficient. It may not be obtained.

  In addition, the dispersible color material used in the present invention has a merit that the chargeable resin pseudo fine particles are fixed to the color material. As a result, the specific surface area of the dispersible color material increases depending on the form, and much of the color material surface It is mentioned that the charge of the chargeable resin pseudo fine particles can be distributed on the surface. As a result, since the dispersible color material has a high specific surface area, the charge of the chargeable resin pseudo fine particles can be converted to the surface charge of the dispersible color material with extremely high efficiency. That is, the form of the dispersible color material used in the present invention is a form in which more surface charges are more efficiently arranged on the surface of the dispersible color material. High dispersion stability can be imparted even when the substantial acid value or amine value of the resin component is smaller than in the form of coating with a resin.

  In general, organic pigments are insolubilized (pigmented) by crystallization of coloring material molecules by strong interaction. In the case of a dispersible color material in which the color material used in the present invention is an organic pigment, as described above, a plurality of interaction points are distributed at the interface between the chargeable resin pseudo fine particles and the color material. The functional resin pseudo fine particles 11 are fixed across several colorant molecules 1a in the pigment particles (see FIG. 5). Therefore, the “pigment peeling” caused by locally hydrophilizing the colorant molecule 1a by the hydrophilic group 12 as described in FIGS. 6A and 6B does not occur in the present invention. Preferably, when an organic pigment is used as a color material, the size of the chargeable resin pseudo fine particles is controlled to be within a range smaller than the dispersed particle diameter of the pigment and larger than the color material molecule. An organic pigment dispersible colorant imparted with high dispersibility without breaking the crystal structure can be obtained.

  In the present invention, the state in which the coloring material “fixes” the chargeable resin pseudo fine particles can be simply confirmed by a technique involving the following three stages of separation. First, in the first separation, the color material to be confirmed is separated from other water-soluble components (including water-soluble resin components) contained in the ink or water dispersion, and then the second In the separation, the coloring material and the water-insoluble resin component contained in the precipitate in the first separation are separated. Furthermore, in the third separation, the weakly adsorbed resin component is separated from the dispersible colorant fixing the charged resin pseudo fine particles, and the quantitative determination of the resin component contained in the third separation supernatant, Then, the fixation of the coloring material and the chargeable resin pseudo fine particles is confirmed by comparing the precipitate of the second separation and the precipitate of the third separation.

  Specifically, for example, it can be confirmed under the following conditions. Take 20 g of the ink or water dispersion in which the color material is dispersed, adjust the total solid content to about 10%, and use a centrifuge to perform the first test at 12,000 rpm for 60 minutes. Separation. Of the separated substances, the lower sediment containing the coloring material is redispersed in pure water approximately three times the amount of the sediment, and then the second sediment is obtained at 80,000 rpm for 90 minutes. Perform separation. The lower layer containing the color material is subjected to the third separation again under the condition of 80,000 rotations and 90 minutes by redispersing the sediment of the lower layer containing the color material in 3 times the amount of pure water. Remove the sediment. The sediment in the second separation and the sediment in the third separation were each taken to have a solid content of about 0.5 g and dried under reduced pressure at 30 ° C. for 18 hours using a scanning electron microscope. Observe at 50,000 times. Then, it was confirmed that the observed dispersible colorant had a plurality of fine particle-like substances or fine aggregates equivalent thereto attached to the surface, and the respective sediments from the second separation and the third separation. If it has the same form, it is judged that this coloring material has fixed the resin pseudo fine particles. Further, the upper layer supernatant in the third separation is gently taken from the top so as to be about half the volume, and the solid content mass is calculated from the mass change before and after drying at 60 ° C. for 8 hours. If it is less than 1%, it is considered that the resin pseudo fine particles are not detached from the dispersible color material, and it can be determined that the dispersible color material fixes the resin pseudo fine particles.

  The above-described separation conditions are preferable examples, and any other separation method or separation condition can be used as long as the method achieves the purpose of the first separation and the second and third separations described above. It can be applied as a method for determining whether or not it is a dispersible colorant used in the above. That is, the first separation is for the purpose of separating the color material contained in the ink and water dispersion and the resin component adsorbed thereto, and the water-soluble component, and the second separation is the color material. The purpose is to separate the resin component adhering to the coloring material and the other resin component adsorbing to the coloring material. Furthermore, the third separation is intended to confirm that the resin component adhering to the color material is not detached. Of course, as long as the separation method achieves the respective purposes of the first, second, and third separations, any other separation method that is publicly known or newly developed may be used. Moreover, it is applicable even if it is at least.

  The second feature of the dispersible colorant used in the present invention is that it is a dispersible colorant that can be dispersed alone in an aqueous medium in a state where the water-insoluble colorant 1 has the chargeable resin pseudo fine particles 2 fixed thereto. It is in. As described above, the dispersible colorant used in the present invention is essentially a self-dispersing agent that can be stably dispersed in water and water-based inks without the aid of other surfactants or polymer dispersants. It is a sex color material. This definition and determination method will be described in detail later. Therefore, the dispersible colorant used in the present invention is added with a polymer dispersant or other resin component or surfactant component that may be released for a long term for the purpose of stabilizing the dispersion of the colorant. There is no need. As a result, when the dispersible color material used in the present invention is used as a water-based ink, the degree of freedom of design regarding components other than the dispersible color material is increased. For example, the permeability of ink such as plain paper is increased. It is also possible to obtain a water-based ink that can obtain a sufficiently high printing density even on a high recording medium.

  The self-dispersibility of the dispersible colorant used in the present invention can be confirmed as follows, for example. The ink or water dispersion in which the color material is dispersed is diluted 10-fold with pure water, and concentrated to the original concentration using an ultrafiltration filter having a molecular weight cut off of 50,000. This concentrated solution is separated in a centrifuge at 12,000 rpm for 2 hours, and the sediment is taken out and redispersed in pure water. At this time, it is judged that what the sediment can redisperse well has self-dispersibility. Whether or not it is well re-dispersed depends on whether it is uniformly distributed visually, or if there is no noticeable sediment during standing for 1 to 2 hours, or if it is shaken lightly It can be comprehensively judged from the fact that the average particle size is less than twice the particle size before operation when the dispersed particle size is measured by the dynamic light scattering method.

  As described above, the dispersible colorant used in the present invention takes a form having a high specific surface area by fixing the chargeable resin pseudo fine particles, and has a large amount of charges on its vast surface. Realize excellent storage stability. Therefore, more preferable results can be obtained when the chargeable resin pseudo fine particles are scattered in large numbers and fixed to the color material. In particular, it is desirable that there is a certain distance between the adhering charged resin pseudo fine particles, and it is preferably distributed uniformly. More preferably, it is desirable that a part of the color material particle surface is exposed between the chargeable resin pseudo fine particles. Such a form is confirmed by observing the water-based ink according to the present invention with a transmission electron microscope or a scanning electron microscope. That is, a plurality of charged resin pseudo fine particles fixed to the color material surface are fixed at a certain distance, or the color material surface is exposed between the fixed charged resin pseudo fine particles. The state can be observed. In addition, the charged resin pseudo fine particles are sometimes close to each other, and in some cases, may be observed to be fused, but even in this case, there is a distance between the charged resin pseudo fine particles as a whole. If the surface of the coloring material is exposed and these states are distributed, it is considered that the charged resin pseudo fine particles are scattered and fixed to the coloring material. It will be apparent to those skilled in the art.

  Furthermore, it has been clarified that the water-based ink containing the dispersible colorant having the above-described characteristics used in the present invention exhibits excellent quick drying on the recording medium. The reason for this is not clear, but is thought to be based on the following mechanism. As described above, the dispersible color material is dispersed in the ink in a form in which charged resin pseudo fine particles are fixed to the color material surface. When this ink reaches the recording medium, the aqueous solvent in the ink (hereinafter referred to as “ink solvent”) is pores on the recording medium due to capillary action (in the case of plain paper, voids between cellulose fibers; In case of glossy paper, it is absorbed into the pores of the receiving layer) At this time, the dispersible color material used in the present invention has many fine gaps due to the morphological characteristics of the charged resin pseudo fine particles interspersed at portions where the color materials are in contact with each other. For this reason, a capillary phenomenon acts on the ink solvent existing between the color materials, and it is quickly absorbed into the recording medium. In the water-based ink according to the present invention, the use of the dispersible colorant in the form in which the chargeable resin pseudo fine particles are scattered on the surface shows more preferable quick drying. Is expected to be achieved.

  According to the study by the present inventors, at this time, by adding a specific salt such as organic ammonium mentioned above to the ink solvent, the ink solvent penetrates into the recording paper and the water evaporates. It was found that the salt concentration in the ink solvent suddenly increased, and as a result, the pigment dispersion stability was impaired and pigment aggregation occurred. That is, by adding a specific salt into the ink, insoluble colorants such as pigments can be prevented from bleeding along the fibers of the recording paper or penetrating into the recording paper, so that there is little bleeding. It is possible to form an image realizing high quality character quality and high color development. In particular, in the present invention, the aggregation of the colorant is performed very efficiently. The reason can be estimated as follows. Since ordinary resin dispersants and the like extend from the colorant toward the dispersion medium, steric hindrance is likely to occur between the colorants even if the charge is lost by the salt. On the other hand, since the chargeable resin pseudo fine particles of the present invention are in the form of particles, the apparent particle size of the colorant becomes smaller. Therefore, after the charge of the chargeable resin pseudo fine particles is lost by the salt, It is difficult to cause steric hindrance.

  Here, as described above, when the surface of a water-insoluble colorant such as a pigment in a state where the charged resin fine particles are not fixed has a high hydrophobic characteristic, the interface added to the ink solvent is used. The dispersing agent such as the water-soluble polymer used in the production of the activator and the dispersible colorant used in the present invention is adsorbed on the pigment surface, and this causes the fast drying of the dispersible colorant to be inhibited. It may be possible. In order to prevent such harmful effects caused by adsorption of the dispersant, a pigment having a high surface hydrophilicity is selected as a coloring material, or the pigment surface is coated with a hydrophilic compound in the finishing process at the time of pigment production. Alternatively, it is effective to use a pigment in which the ratio of oxygen atoms on the pigment surface is increased by wet or dry oxidation of the pigment in advance.

Next, each component constituting the dispersible colorant used in the present invention will be described.
[Color material]
The color material which is a constituent component of the dispersible color material used in the present invention will be described below. As the color material used in the present invention, among color materials known or newly developed, it is desirable to use a color material that is insoluble in water and can be stably dispersed in water together with a dispersant. Examples of such materials include hydrophobic dyes, inorganic pigments, organic pigments, metal colloids, and colored resin particles. Preferably, a coloring material having a dispersed particle size in the range of 0.01 to 0.5 μm (10 to 500 nm), particularly preferably in the range of 0.03 to 0.3 μm (30 to 300 nm) is used. A dispersible color material using a color material dispersed in this range is a preferable dispersible color material that gives an image having high coloring power and high weather resistance when used as an aqueous ink.

  In the present invention, examples of the inorganic pigment that can be effectively used for the coloring material include carbon black, titanium oxide, zinc white, zinc oxide, tripone, iron oxide, cadmium red, molybdenum red, chrome vermilion, and molybdate orange. , Yellow lead, chrome yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, pyridian, cobalt green, titanium cobalt green, cobalt chrome green, ultramarine blue, ultramarine blue, bitumen, cobalt blue, cerulean blue, manganese violet, Examples include cobalt violet and mica.

  Examples of organic pigments that can be effectively used in the present invention include azo, azomethine, polyazo, phthalocyanine, quinacridone, anthraquinone, indigo, thioindigo, quinophthalone, benzimidazolone, Various pigments such as indoline and isoindolinone are listed.

Other organic insoluble colorants that can be used in the present invention include, for example, azo, anthraquinone, indigo, phthalocyanine, carbonyl, quinoneimine, methine, quinoline, nitro, etc. Dyes. Of these, disperse dyes are particularly preferable.
At this time, as described in the third, fourth, and fifth aspects, the pigment surface is more preferably a pigment having a hydrophilic surface in which oxygen atoms are exposed. Such a hydrophilic surface does not adsorb the surfactant or polymer dispersant applied during the production of the dispersion or in the ink formulation, and the pigment is formed only by the electrostatic repulsive force of the charged resin pseudo fine particles. Dispersed, the quick-drying property is extremely improved and it is difficult to bleed.

[Charged resin pseudo fine particles]
The charged resin pseudo fine particles, which are another component of the dispersible color material used in the present invention, are substantially insoluble in water, and the color material to be fixed in water (or in ink). The dispersion unit (dispersion particle size) is small, and is defined as a fine body formed by aggregating resin components having a sufficiently high degree of polymerization. The form of the minute body is pseudo close to a sphere, or a plurality of minute bodies (chargeable resin pseudo fine particles) are arranged within a certain range. It is preferable that the resin components constituting the chargeable resin pseudo fine particles are physically or chemically cross-linked with each other. Whether the resin components constituting the chargeable resin pseudo fine particles are cross-linked with each other can be confirmed by using, for example, the following method. The resin component constituting the chargeable resin pseudo fine particles is estimated in advance by a known analysis method, and a linear polymer having the same chemical structure (or the same monomer unit composition) is synthesized by solution polymerization, On the other hand, when the chargeable resin pseudo fine particles and the polymer are immersed in an organic solvent, which is a good solvent, and their solubility is compared, the chargeability is determined when the solubility of the chargeable resin pseudo fine particles is lower than the solubility of the polymer. It is confirmed that the interior of the resin pseudo fine particles is crosslinked.

  In another preferred embodiment, when the dispersed particle diameter of the chargeable resin pseudo fine particles in water can be measured by, for example, the dynamic light scattering method, the average value of the dispersed particle diameter is preferably 10 nm. It is desirable to be in the range of 200 nm or more. Furthermore, from the viewpoint of long-term storage stability of the dispersible colorant, it is more preferable that the polydispersity index of the dispersed particle diameter is suppressed to less than 0.2. When the center value of the dispersed particle diameter is larger than 200 nm or when the polydispersity index is larger than 0.2, the original purpose of finely dispersing and stabilizing the coloring material may not be sufficiently achieved. Further, when the average value of the dispersed particle diameter is smaller than 10 nm, the form as the chargeable resin pseudo fine particles cannot be sufficiently maintained, and the resin is easily dissolved in water, so that the merit of the present invention cannot be obtained. There is a case. On the other hand, in the range of 10 nm or more and 200 nm or less, the particle diameter is smaller than the color material particles themselves, so that the dispersion stabilization of the color material by the fixation of the chargeable resin pseudo fine particles in the present invention is effectively expressed. . The above preferred embodiment is the same when the dispersed particle size of the chargeable resin pseudo fine particles is not measurable. In that case, for example, the average diameter of the chargeable resin pseudo fine particles in the electron microscope observation is as described above. It is considered to be a preferred range or a range equivalent thereto.

  When the color material is an organic pigment, in addition to the above range, as described above, the charged resin pseudo fine particles are smaller than the pigment dispersed particle size and larger than the color material molecule. It is particularly desirable because a dispersible colorant having a structurally extremely stable and high dispersibility can be obtained.

  The chargeability in the present invention refers to a state in which a functional group that is ionized in some form in the aqueous medium itself is retained, and is desirably self-dispersible by the chargeability. Therefore, whether or not it is a chargeable resin pseudo fine particle is determined by a method of measuring the surface zeta potential of the chargeable resin pseudo fine particle by a publicly known and arbitrary method, a potentiometric titration by a method as described later, and a functional group. A method for calculating the density, a method for confirming the dependency of dispersion stability on the electrolyte concentration by adding an electrolyte to the aqueous dispersion of the charged resin pseudo fine particles, or a chemical structure analysis of the charged resin pseudo fine particles as a known method The method can be confirmed by any one of the methods of examining the presence or absence of an ionic functional group.

  The resin component constituting the chargeable resin pseudo fine particles may be any resin component such as any commonly used natural or synthetic polymer, or a newly developed polymer for the present invention, without limitation. . Examples of resin components that can be used include acrylic resins, styrene / acrylic resins, polyester resins, polyurethane resins, polyurea resins, polysaccharides, and polypeptides. In particular, from the standpoint that it can be used generally and the functional design of the chargeable resin pseudo fine particles can be easily performed, a polymer or copolymer of a monomer component having a radical polymerizable unsaturated bond, such as an acrylic resin or a styrene / acrylic resin, is used. A polymer can be preferably used.

  Examples of the monomer having a radically polymerizable unsaturated bond preferably used in the present invention (hereinafter referred to as a radically polymerizable monomer or simply a monomer) include the following. Classified as hydrophobic monomers, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylate-n-propyl, acrylate-n-butyl, acrylate-t-butyl, benzyl acrylate, methyl methacrylate (Meth) acrylic acid esters such as ethyl methacrylate, isopropyl methacrylate, methacrylate-n-propyl, methacrylate-n-butyl, isobutyl methacrylate, tert-butyl methacrylate, tridecyl methacrylate, benzyl methacrylate, etc. Styrene monomer such as styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, p-tert-butyl styrene, etc .; itaconate such as benzyl itaconate; dimethyl maleate, etc. Such as Esters; fumaric acid such as fumaric acid esters such as dimethyl acrylonitrile, methacrylonitrile, vinyl acetate, and the like.

  In addition, those classified as the following hydrophilic monomers are also preferably used. For example, monomers having an anionic group include, for example, monomers having a carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid, and the like. A monomer having a sulfonic acid group such as a salt, styrene sulfonic acid, sulfonic acid-2-propylacrylamide, acrylic acid-2-ethyl sulfonate, methacrylic acid-2-ethyl sulfonate, butyl acrylamide sulfonic acid, and the like; And monomers having a phosphonic acid group such as ethyl methacrylate-2-phosphonate and ethyl acrylate-2-phosphonate. Among these, it is particularly preferable to use acrylic acid and methacrylic acid.

[Synthesis of chargeable resin pseudo fine particles and fixation to coloring material]
The method for synthesizing the chargeable resin pseudo fine particles and the method for fixing to the color material are carried out by a method for synthesizing the charge resin pseudo fine particles and a method for combining the charge resin pseudo fine particles and the color material. Can do. On the other hand, the present inventors, as a result of intensive studies, are dispersible colorants having the colorant and the chargeable resin pseudo fine particles smaller than the colorant, which are the characteristics of the present invention. It came to invent the manufacturing method which can obtain easily the dispersible color material of the state which this chargeable resin pseudo fine particles adhere to the material. Hereinafter, a suitable method for producing a dispersible color material, from which the dispersible color material used in the present invention can be easily obtained, will be described.

  As a result of the study by the present inventors, it has been clarified that the dispersible colorant used in the present invention having the above-described characteristics can be produced very simply by applying the aqueous precipitation polymerization method under the following conditions. It was. In such a production method, first, a water-insoluble colorant is dispersed with a dispersant to prepare a dispersed aqueous solution of the water-insoluble colorant. Next, in this dispersed aqueous solution, the chargeable resin pseudo fine particles are fixed to the coloring material by a step of aqueous precipitation polymerization of the radical polymerizable monomer using an aqueous radical polymerization initiator. The dispersible colorant obtained through this aqueous precipitation polymerization process is a water-insoluble color in which the chargeable resin pseudo fine particles synthesized in the aqueous precipitation polymerization process are strongly and firmly adhered to the colorant. It becomes a material and has excellent dispersion stability by itself. Further, in the above aqueous precipitation polymerization process, the characteristics of the chargeable resin pseudo fine particles can be easily controlled to the preferred form as described above. And the charge resin pseudo fine particles are satisfactorily achieved. Hereinafter, preferred embodiments of the manufacturing method will be described in more detail.

(Dispersion of water-insoluble colorant)
First, the water-insoluble colorant preferably used in the present invention as described above is dispersed with a dispersant to obtain an aqueous dispersion. As the dispersant for dispersing the coloring material in the aqueous solution, any of ionic, nonionic, etc. can be used, but from the viewpoint of maintaining dispersion stability in the subsequent polymerization step, the polymer dispersant or water-soluble It is desirable to use a polymer. In particular, a radically polymerizable monomer that is sufficiently water-soluble and that serves as an adsorption site to the oil droplet interface of the radically polymerizable monomer surface and the hydrophobic monomer added in the polymerization process is preferably used. It is done. More preferably, at least one of the hydrophobic monomers used in the subsequent polymerization step is present as a unit constituting the dispersing agent, so that the color of the charged resin pseudo fine particles in the subsequent polymerization step. This is preferable from the viewpoint of easily inducing adhesion to the material.

  The production method of the polymer dispersant and the water-soluble polymer that functions as a dispersant that can be used in the present invention is not particularly limited. For example, a monomer having an ionic group and another polymerizable monomer are non-polymerized. It can manufacture by making it react in the presence or absence of a catalyst in a reactive solvent. In particular, a styrene / acrylic polymer compound obtained by polymerizing a monomer having an ionic group as described above and a styrene monomer as essential components, or a monomer having an ionic group, and the number of carbon atoms is 5. From the ionic group-containing acrylic polymer compound obtained by polymerizing the above (meth) acrylic acid ester monomer as an essential component, it has been clarified that good results can be obtained by using a dispersant selected. . At this time, when the obtained dispersible colorant is intended to have an anionic group in particular, an anionic dispersant, while the obtained dispersible colorant is intended to have a cationic group in particular. In this case, it is desirable to select a dispersant having a cationic group or a nonionic dispersant.

  From the viewpoint of coexistence of promoting the fixation of the chargeable resin pseudo fine particles to the coloring material in the subsequent aqueous precipitation polymerization process and maintaining the dispersion stability of the coloring material in the polymerization process. It is also desirable to use those having an acid value of 100 or more and 250 or less in the case of using an acid, and those having an amine value of 150 or more and 300 or less in the case of using a cationic dispersant. When the acid value and the amine value are smaller than these ranges, the affinity between the hydrophobic monomer and the dispersant becomes higher than the affinity between the colorant and the dispersant during the aqueous precipitation polymerization, and the chargeable resin pseudo In some cases, the dispersing agent may be detached from the surface of the color material before the fine particles are fixed to the color material, and the dispersed state cannot be maintained. In addition, if the acid value and amine value are larger than these ranges, the excluded volume effect of the dispersant on the surface of the color material and the electrostatic repulsion force become too strong, so that the chargeable resin pseudo fine particles adhere to the color material. May be inhibited. When using an anionic dispersant, it is preferable to select a dispersant having a carboxyl group as an anionic group from the viewpoint of not inhibiting the adhesion of the resin fine particles to the colorant.

  In the process of making a water-insoluble colorant into a dispersion aqueous solution with a dispersant, the colorant preferably has a dispersed particle diameter in the range of 0.01 μm to 0.5 μm (10 nm to 500 nm), particularly preferably 0.03 μm or more. Disperse in a range of 0.3 μm or less (30 nm or more and 300 nm or less). The dispersed particle diameter in this process largely reflects the dispersed particle diameter of the dispersible colorant to be obtained, and the above range is preferable from the viewpoint of the above-mentioned coloring power, image weather resistance, and dispersion stability.

  The dispersion particle size distribution of the water-insoluble colorant used in the present invention is preferably monodispersed as much as possible. In general, the particle size distribution of the dispersible colorant obtained by fixing the charged resin pseudo fine particles becomes narrower than the particle size distribution of the dispersed aqueous solution before the polymerization step shown in FIG. Although it tends to be, it basically depends on the particle size distribution of the dispersed aqueous solution. It is also important to narrow the particle size distribution of the color material in order to surely induce fixation due to heteroaggregation of the color material and the charged resin pseudo fine particles. According to the study by the present inventors, when the polydispersity index of the color material is in the range of 0.25 or less, the dispersion stability of the obtained dispersible color material becomes excellent.

  Here, the particle size of the colorant in a dispersed state varies depending on various measurement methods. Particularly, the organic pigment is very small when it is a spherical particle, but in the present invention, the colorant is moved by ELS-8000 manufactured by Otsuka Electronics Co., Ltd. The average particle size and the polydispersity index obtained by the measurement based on the dynamic light scattering method and cumulant analysis were used.

  The method for dispersing the water-insoluble coloring material in water may be any method that uses a dispersing agent as described above, among the methods in which the coloring material can be stably dispersed in water under the conditions described above. It is not limited to any method that is used. Alternatively, a dispersion method newly developed for the present invention may be used. In general, for example, when the water-insoluble colorant is a pigment, the addition amount of the polymer dispersant to be used is suitably 10% by mass or more and 130% by mass or less based on the pigment.

  Examples of the dispersion method of the color material used in the present invention include, for example, a dispersion machine such as a paint shaker, a sand mill, an agitator mill, and a three roll mill, a high-pressure homogenizer such as a microfluidizer, a nanomizer, and an optimizer, an ultrasonic dispersion machine, and the like. Any dispersion method that is generally used for each color material is not limited.

(Aqueous precipitation polymerization)
Subsequently, a preferred embodiment of the aqueous precipitation polymerization, which is a step of synthesizing the chargeable resin pseudo fine particles, which is a feature of the present invention, and fixing it to the coloring material will be described. In addition, this invention is not restrict | limited at all by embodiment described below. FIG. 2 is a process diagram schematically showing a process flow of the manufacturing method. The process up to obtaining a dispersible colorant by this step is considered as follows. First, as shown in FIG. 2A, a dispersed aqueous solution in which the coloring material 1 is dispersed in the aqueous solution by the dispersant 3 is prepared. At this time, the coloring material is dispersed and stabilized by adsorption of the dispersing agent, and this adsorption is in a thermal equilibrium state. Next, the temperature of the dispersion aqueous solution prepared in FIG. 2A is raised while stirring, and the monomer component 4 is added to the dispersion together with, for example, the aqueous radical polymerization initiator 5 (see FIG. 2B). The added aqueous radical polymerization initiator cleaves when heated to generate radicals, and among the monomer components added to the aqueous dispersion, a small amount of the hydrophobic monomer dissolved in the aqueous phase and the aqueous phase Contributes to the reaction with the water-soluble monomer.

  FIG. 3 is a schematic diagram illustrating a process until the monomer 4 is polymerized to produce a dispersible colorant. When the reaction of the monomer 4 as described above proceeds, the oligomer 7 generated by the polymerization reaction of the monomer component becomes insoluble in water and precipitates from the aqueous phase to become a precipitate 8. However, since the oligomer 7 deposited at this time does not have sufficient dispersion stability, the charged resin pseudo fine particles 2 are formed together. Further, the charged resin pseudo fine particles 2 cause hetero-aggregation with the hydrophobic surface of the color material in the aqueous dispersion as a nucleus, and the resin component constituting the surface of the color material 1 and the charge resin pseudo fine particles 2 has a hydrophobic interaction. Strongly adsorbed by. At this time, the polymerization reaction continues to proceed inside the chargeable resin pseudo fine particles 2, and changes to a more energetically stable form while increasing the adsorption point with the colorant 1. At the same time, since the inside of the chargeable resin pseudo fine particles 2 is highly physically crosslinked, the form that adsorbs the color material 1 most stably is fixed and is in a fixed state. On the other hand, the coloring material 1 is stabilized by fixing the plurality of chargeable resin pseudo fine particles 2, and the dispersant 3 in an equilibrium state is detached from the surface of the coloring material 1.

  FIG. 4 shows a schematic diagram of the chargeable resin pseudo fine particles 2 obtained as described above on the fixing interface side with the coloring material 1. As shown in FIG. 4, since the charged resin pseudo fine particles, which are aggregates of resin components, are present in an arbitrarily distributed hydrophilic monomer unit 9-1, hydrophobic monomer unit 9-2, etc. The surface energy has a distribution, and there are many adsorption points 10 that coincide with the surface energy of the color material.

  FIG. 5 shows an enlarged schematic view of the fixing interface portion between a part of the chargeable resin pseudo fine particles 11 and the part 1a of the color material particles. The interface 11 of the chargeable resin pseudo fine particles is shown in FIG. While adsorbing the adsorbing point 10, it takes a form corresponding to the surface shape of the part 1a of the color material and adheres stably. As described above, since the polymerization reaction is proceeding in the chargeable resin pseudo fine particles also in this process, fixation to the coloring material is achieved by fixing the adsorption in a stabilized form. Through the above-described process, the dispersible color material having the above-described configuration is easily formed (see FIG. 2D). At this time, in a system in which the chargeable resin pseudo fine particles have sufficient surface charge to achieve self-dispersibility, the charge resin pseudo fine particles are interspersed in the process of adsorption and fixation to the coloring material by heteroaggregation. When the electrostatic repulsive force acts mutually, the chargeable resin pseudo fine particles are scattered and fixed to the color material, and the preferred form described above is obtained.

  The polymerization reaction conditions vary depending on the properties of the polymerization initiator, the dispersant, and the monomer to be used. For example, the reaction temperature is 100 ° C. or lower, preferably 40 ° C. or higher and 80 ° C. or lower. The reaction time is 1 hour or more, preferably 6 hours or more and 30 hours or less. The stirring speed during the reaction is from 50 rpm to 500 rpm, preferably from 150 rpm to 400 rpm.

  In the above-described steps, particularly when the chargeable resin pseudo fine particles are obtained by polymerizing a monomer component containing at least one kind of hydrophobic monomer and at least one kind of hydrophilic monomer, the monomer component is preferably an aqueous solution. It is desirable to drop it into a dispersed aqueous solution of a water-insoluble colorant that contains a radical polymerization initiator in advance. Alternatively, it is also desirable to add the water-insoluble colorant dropwise at the same time or separately from the aqueous radical polymerization initiator in the aqueous dispersion. In order to uniformly obtain desired charged resin pseudo fine particles from a mixture of monomers having different properties such as a hydrophobic monomer and a hydrophilic monomer, it is desirable to always keep the copolymerization ratio of the monomers having different properties constant. . When the mixture of monomers is added to the polymerization system in excess of the amount of monomer consumed in the polymerization reaction within a certain time, only a specific monomer species is polymerized in advance, and the remaining monomers are polymerized in advance. There is a tendency to polymerize after the consumed monomer is consumed, and in this case, a large non-uniformity occurs in the properties of the generated chargeable resin pseudo fine particles. Among the charged resin pseudo fine particles generated in this way, those having a particularly large hydrophilic monomer component content may not be able to adhere to the surface of the color material.

  Furthermore, when the resin component has a high content of the hydrophilic monomer component, it may not be precipitated due to its high hydrophilicity, and may remain in the system as a water-soluble resin component without forming charged resin pseudo fine particles. is there. On the other hand, by dropping the monomer component into a water-insoluble colorant-dispersed aqueous solution containing an aqueous radical polymerization initiator, the copolymerization ratio between the hydrophobic monomer and the hydrophilic monomer is always kept constant. Chargeable resin pseudo fine particles composed of a copolymerization ratio can be obtained uniformly.

  In addition, especially when anionic monomers such as acrylic acid and methacrylic acid are added to the polymerization system as hydrophilic monomers, they may become partially unstable depending on the characteristics of the polymer dispersant in which the colorant is dispersed. , May cause aggregation. In order to prevent this, it is also a preferred embodiment that the anionic monomer is neutralized in advance and added in the form of sodium salt or potassium salt.

  When preparing a water-based ink using the water-insoluble color material obtained by the above-described process and having the chargeable resin pseudo fine particles fixed to the color material according to the present invention, in addition to the above-described process, further purification is performed. It is desirable to perform processing. In particular, in the above, it is possible to carry out purification treatment on unreacted polymerization initiator, monomer component, dispersant, water-soluble resin component that has not been fixed, and chargeable resin pseudo fine particles, etc. Is important in maintaining high. As a purification method to be used, an optimum one may be selected from generally used purification methods. For example, purification using a centrifugal separation method or an ultrafiltration method is a preferred embodiment.

  Through the above-described steps, a dispersible color material in which charged resin pseudo fine particles made of a desired copolymer are fixed to the surface of the color material can be obtained by controlling many control factors. In particular, when an anionic monomer is used for the purpose of high dispersion stability, the dispersible colorant having undergone the process of the present invention has a large surface even if the amount of the anionic monomer used in the above process is relatively small. A functional group density can be obtained and high dispersion stability can be imparted. As a result, it becomes possible to increase the dispersion stability of the chargeable resin pseudo fine particles without impairing the long-term storage stability.

  Although this reason is not clear, the present inventors consider as follows. Polymerization is initiated by radicals generated in water, and when oligomers are precipitated to form charged resin pseudo fine particles, the portion having a large amount of anionic monomer-derived components is preferentially on the water phase side, that is, charged resin pseudo fine particles. Oriented near the surface. This state is maintained even after the chargeable resin pseudo fine particles are fixed to the color material. In the dispersible color material used in the present invention having a structurally large specific surface area, an anionic property derived from an anionic monomer component is further provided. Many groups are present, and as a result, the dispersible colorant obtained by the above-described production method is expected to be stabilized with fewer anionic monomer components.

[Water-based ink]
The water-based ink according to the present invention includes the dispersible color material described above. When the coloring material to be used is a pigment, the pigment content is generally 0.1% by mass or more and 20% by mass or less, preferably 0.3% by mass or more and 15% by mass or less with respect to the ink. Further, as the aqueous medium, water or a mixed medium containing a water-soluble organic solvent as necessary is also preferable. Further, it may contain a penetrant, an antiseptic, an antifungal agent and the like for helping the permeability to the recording medium.

  As shown in FIG. 1, the dispersible color material used in the present invention is present in the ink in a state where the chargeable resin pseudo fine particles 2 are fixed to the surface of the color material 1. Therefore, the color material adheres to the recording medium and the adjacent color material on the recording paper via the chargeable resin pseudo fine particles fixed to the surface. Accordingly, the printed matter obtained using the water-based ink of the present invention has excellent scratch resistance. As a more preferred embodiment, in addition to the above-described configuration, a water-based ink in which self-dispersing resin fine particles are dispersed is present, which is usually difficult for water-insoluble colorants such as pigments. High gloss printing is possible. In this case, it is more preferable that the charged resin pseudo fine particles (A) fixed to the coloring material and the self-dispersing resin fine particles (B) dispersed in the ink are present. The monomer component constituting the chargeable resin pseudo fine particles (A) and the monomer component constituting the self-dispersing resin fine particles (B) comprise one or more types of common monomer components. Since the affinity between the dispersible colorant to which the pseudo fine particles (A) are fixed and the self-dispersing resin fine particles (B) is increased and the adhesive force is increased, in particular, according to the above-described aspect, on the glossy medium. The scratch resistance of the formed printed matter is greatly improved.

  Further, in the case of using a pigment as the coloring material, the ratio of the pigment and the chargeable resin pseudo fine particles (resin mass / pigment mass = B / P) is in the range of 0.3 or more and 4.0 or less. It can be said that this is a desirable embodiment of the present invention in order to improve the scratch resistance of the printed matter formed of the color material. By setting the B / P ratio to be 0.3 or more, it is possible to impart excellent scratch resistance to the printed matter by improving the adhesion between the color materials and between the color material and the recording medium. In particular, in the case of aqueous ink using a dispersible color material formed by fixing charged resin pseudo fine particles comprising a copolymer component having a glass transition temperature of −40 ° C. or more and 60 ° C. or less, the film formation Can be exhibited more effectively, and the result is that the scratch resistance of glossy paper is further improved. When B / P is significantly larger than 4.0, the ink becomes highly viscous as a whole. In particular, when used in an ink jet recording apparatus, ejection stability may be impaired. In addition, since the amount of resin is extremely large relative to the color material, the color density of the color material on the recording medium is hindered, and the print density may not be sufficiently obtained. By controlling the B / P value within the range of 0.3 to 4.0, the water-based ink having excellent scratch resistance and compatible with ejection stability in the ink jet recording apparatus can be obtained. it can.

  The resin mass as used herein refers to the total amount of the chargeable resin pseudo fine particles contained in the ink according to the present invention, and may include other resin components that are clearly strongly adsorbed on the pigment surface. is there. However, the water-soluble resin component that can be easily separated from the pigment is not included.

  The above-mentioned B / P value can be generally obtained by differential thermogravimetric analysis, but in the present invention, it is a value measured and calculated with TGA / SDTA851 manufactured by METTTLER. That is, in the present invention, the sediment obtained by centrifuging the dispersible colorant or the water-based inkjet recording ink containing the colorant according to the present invention at 80,000 rpm for 2 hours is dried and weighed. The mass change before and after the respective decomposition temperatures of the pigment and the resin component when the temperature was raised in a nitrogen atmosphere or in the air was calculated, and B / P was calculated.

[Recorded image]
The ink according to the present invention can be suitably used for recording using an ink jet recording apparatus as described later. The recording medium used at this time can be used without limitation even if it is a medium capable of ink jet recording. In the ink jet recording image formed at this time, the dispersible colorant used in the present invention has a preferable form as shown in FIGS. 7 a, b, and c) due to its characteristic shape. (Most preferably only b) or c), but the implementation level includes these simultaneously). a) is likely to occur particularly when the self-dispersing resin fine particles B are further added to the water-based ink according to the present invention, and the charged resin pseudo fine particles so as to fill the irregularities between the coloring materials on the recording medium. Alternatively, by depositing the self-dispersing resin fine particles B, a highly glossy image is realized even on a glossy recording medium. Further, b) shows that the chargeable pseudo fine particles 2 fixed to the respective color materials existing between the adjacent color materials are fixed to each of the adjacent color materials, thereby forming a strong colored film. In this state, a recording image having a high scratch resistance was formed. Furthermore, by making the proportion of the chargeable resin pseudo fine particles fixed to the surface of the color material relatively small, the function of b) is also used while partially allowing the color materials to aggregate. The preferred form is as follows. c) shows the electrostatic repulsive force of the chargeable resin pseudo fine particles (indicated by the arrow 15 in the figure) and the aggregation of the color material surface in the process of aggregation of the dispersible color material in the ink adhered on the recording medium. It shows that the aggregation form is controlled by the balance with the force. By performing such control, it is possible to control image density or ink bleeding due to color material aggregation control on the recording medium.

[Image recording method and recording apparatus]
The dispersible color material used in the present invention and the water-based ink containing the color material are used for an inkjet discharge type head, and also as an ink tank in which the ink is stored or for filling the ink tank. It is also effective as an ink. In particular, the present invention provides an excellent effect in a bubble jet type recording head and recording apparatus among ink jet recording types.

  As for the typical configuration and principle, for example, those performed using the basic principle disclosed in US Pat. Nos. 4,723,129 and 4,740,796 are preferable. . This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or liquid path holding the ink. By applying at least one drive signal corresponding to the recording information and giving a rapid temperature rise exceeding the nucleate boiling to the electrothermal transducer, heat energy is generated in the electrothermal transducer, and the thermal action of the recording head This is effective because the film can be boiled on the surface and, as a result, the drive signals can be made to correspond one-to-one and bubbles in the ink can be formed. By the growth and contraction of the bubbles, ink is ejected through the ejection openings to form at least one droplet. It is more preferable that the drive signal has a pulse shape, because the bubble growth and contraction is performed immediately and appropriately, and thus ink discharge with particularly excellent responsiveness can be achieved. As this pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by adopting the conditions described in US Pat. No. 4,313,124, which is an invention relating to the rate of temperature increase of the heat acting surface.

  As the configuration of the recording head, in addition to the combination configuration (linear liquid channel or right-angle liquid channel) of the discharge port, the liquid channel, and the electrothermal transducer as disclosed in each of the above-mentioned specifications, the heat acting part The present invention is also effective for configurations using US Pat. No. 4,558,333 and US Pat. No. 4,459,600, which disclose configurations in which the lens is disposed in a bending region. In addition, the present invention is also effective for a configuration (Japanese Patent Laid-Open No. 59-123670, etc.) in which a discharge hole is used as a discharge portion of the electrothermal transducer when common to a plurality of electrothermal transducers. . Furthermore, as a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the recording apparatus, the length is set by combining a plurality of recording heads as disclosed in the above specification. Either a satisfying configuration or a single recording head configuration may be used, but the present invention can exhibit the above-described effects more effectively.

  In addition, it is mounted on the main body of the device so that it can be electrically connected to the main body of the device and supplied with ink from the main body of the device. The present invention is also effective when a cartridge type recording head is used. In the present invention, it is preferable to add a recovery means for the recording head, a preliminary auxiliary means, etc. provided as a configuration of the recording apparatus to be applied, because the effects of the present invention can be further stabilized. is there. Specifically, a capping unit for the recording head, a cleaning unit, a pressurizing or suction unit, an electrothermal transducer, a heating element different from this, or a preheating unit using a combination of these, recording and the like Is a preliminary discharge mode for performing another discharge.

  Next, an Example and a comparative example are given and this invention is demonstrated concretely. The present invention is not limited by the following examples unless it exceeds the gist. In the text, “part” or “%” is based on mass unless otherwise specified.

[Example 1]
A recording ink 1 according to Example 1 was prepared as follows. First, a mixed liquid composed of 10 parts of carbon black, 6 parts of glycerin, 10 parts of a styrene-acrylic acid resin dispersant, and 74 parts of water was subjected to a sand mill manufactured by Kanada Rika Kogyo Co., Ltd. at 1,500 rpm for 5 hours. Dispersion was performed to obtain Pigment Dispersion Liquid 1. In the sand mill, zirconia beads having a diameter of 0.6 mm were used, and the filling rate in the pot was 70%. The carbon black used in the present example is Black Pearls 880 (hereinafter abbreviated as BP880) marketed by Cabot Corporation in the United States. The styrene-acrylic acid resin dispersant has a copolymerization ratio of 70:30, Mw. = 8,000, acid value 170 was used. As the styrene-acrylic acid resin dispersant, water and potassium hydroxide equivalent to the above acid value were added in advance and stirred at 80 ° C. to obtain an aqueous solution. The obtained pigment dispersion 1 was stably dispersed with an average dispersion particle size of 98 nm, and the polydispersity index was 0.16.

  Next, 500 parts of the pigment dispersion 1 obtained above was added to each of the following three additive liquids dropwise while stirring with a motor while heating to 70 ° C. in a nitrogen atmosphere. Polymerization was performed for 5 hours. Each additive solution is (1) a monomer mixture comprising 28.5 parts of methyl methacrylate, (2) a mixture liquid comprising a hydrophilic monomer comprising 1.5 parts of acrylic acid, 0.36 parts of potassium hydroxide and 30 parts of water, (3) A mixed solution containing a polymerization initiator composed of 0.05 part of potassium persulfate and 30 parts of water. The obtained dispersion was diluted 10-fold with water and centrifuged at 5,000 rpm for 10 minutes to remove the aggregating component. Then, it further refine | purified by centrifuging on conditions of 12,500 rpm and 2 hours, and the dispersible color material 1 which is a sediment was obtained.

  The dispersible colorant 1 obtained above was dispersed in water, centrifuged at 12,000 rpm for 60 minutes, and then the precipitate re-dispersed in water was dried, and the scanning electron microscope JSM -6700 (manufactured by JEOL Hi-Tech Co., Ltd.) was observed at a magnification of 50,000 times. In the dispersible colorant 1, resin fine particles smaller than carbon black were fixed on the surface of carbon black as the colorant. The condition was observed. In addition, also about the color material after this described in a present Example, the form of the color material was confirmed with the method similar to the above.

The dispersible colorant 1 obtained above is contained in the ink at a concentration of 4%, and the following component composition is mixed with this and further pressurized with a membrane filter having a pore size of 2.5 microns. Filtration was performed to prepare the ink of this example. The total amount of ink was adjusted with water so as to be 100 parts.
・ Glycerol 7 parts ・ Diethylene glycol 5 parts ・ Trimethylolpropane 7 parts ・ Acetylenol EH (trade name: manufactured by Kawaken Fine Chemicals Co., Ltd.) 0.2 part ・ Ammonium benzoate 0.5 part ・ Ion-exchanged water remaining

[Comparative Example 1]
In the ink formulation used in Example 1, a comparative ink was prepared by the same method and formulation as in Example 1 except that ammonium benzoate was not added.

[Evaluation]
Using the inks obtained in Example 1 and Comparative Example 1, a printing test was conducted with a Canon inkjet printer S-700 as follows. Each ink was injected into a BCI-3eBK empty ink tank mounted on S-700, and a printing test was performed as it was. As a result, in the ink of Example 1 containing ammonium benzoate, the character quality and the bleed of the color tone in the boundary area with the color ink (bleed) were compared with the ink of Comparative Example 1 not containing ammonium benzoate. It was much better.

[Example 2]
In Example 1, each ink was prepared in the same manner as in Example 1 except that the amount of ammonium benzoate added was changed from 0.01% to 10.0%. Similarly, bleed characteristics and character quality were evaluated. The results are summarized in Table 1. As a result, when the amount of ammonium benzoate added was less than 0.05%, the effects of improving the character quality and reducing the bleed were slightly inferior to those of Example 1 (“△” in the table). "). On the other hand, when the amount of ammonium benzoate added exceeds 5%, the discharge characteristics deteriorate compared to the case of Example 1, white streaks are likely to occur, or a 60 ° C / 3 day storage test. It has been confirmed that another problem may be caused by adding ammonium benzoate to the ink, such as the generation of a gelled product.

[Example 3]
A dispersible colorant used for the ink was prepared in the same manner as in Example 1 except that the carbon black was changed from BP880 used in Example 1 to NIPEX 180 of Degussa, Germany. Here, in order to compare the surface state of the carbon black used, the surface oxygen amount of the carbon black was measured by the following method. The amount of surface oxygen of carbon black was measured by the following heat loss method. In this method, carbon black is heated for about 10 minutes at 950 ° C. under vacuum, and the amount of surface oxygen is estimated from the weight loss that occurs. That is, the gas generated by heating under the above conditions is carbon monoxide and carbon dioxide, and these gases are caused by carboxyl groups, hydroxyl groups, quinones, etc. present on the carbon surface. It can be said that the greater the weight loss, the greater the amount of surface oxygen. As a result of the measurement, in the case of BP880 used in Example 1, the heat loss was 1.5%, whereas the heat loss of NIPEX180 used in this example was 5%, and the surface of the carbon black It was confirmed that the amount of oxygen was larger than that used in Example 1.

  Using the dispersible color material prepared above, an ink was prepared by the same method and ink formulation as in Example 1. Then, in the same manner as in Example 1, the obtained ink was subjected to a printing test and evaluated for printing. As a result, it was confirmed that better character quality and bleed characteristics can be realized than in the case of the ink of Example 1.

[Example 4]
A dispersible colorant was prepared in the same manner as in Example 1 except that carbon black was changed from BP880 used in Example 1 to wet-oxidized carbon manufactured by Tokai Carbon Co., Ltd. The wet oxidized carbon used in this example is obtained by oxidizing the surface of carbon black in an aqueous phase using an oxidizing agent. As in the case of Example 3, when the surface oxygen amount of this wet oxidized carbon was measured, the loss on heating of the carbon was 15%. The surface oxygen amount of the carbon used in this example was the same as in Example 1 and It was confirmed that it was much more than that used in 2.

  Using the dispersible colorant prepared above, an ink was prepared according to the same ink formulation as in Example 3. When printing was performed in the same manner as in Example 1, it was possible to realize extremely good character quality and bleed characteristics as compared with Examples 1 to 3.

[Example 5]
A dispersible colorant was prepared in the same manner as in Example 1 except that CABOJET-200 manufactured by Cabot Corporation of the United States was used as the carbon black raw material. This carbon black has a structure in which a carbonyl group is added to the carbon surface. Although the production method is one of the wet oxidation methods, there is a practical problem that the cost is high because the reaction is not an oxidation reaction using a simple oxidizing agent.

  An ink was prepared in the same manner as in Example 1 (however, the amount of ammonium benzoate added was 1%), and printing was performed in the same manner as in Example 1 using the obtained ink. Can be printed. The degree of printing was equivalent to that of an ink obtained by dispersing CABOJET-200 with a dispersant (hereinafter referred to as CABOJET-200 ink), and a recorded matter with better printing quality was obtained.

  The character formed with the ink obtained in this example and the character printed with the CABOJET-200 ink were each subjected to a rubbing test with a finger and a marker resistance test with a marker pen. In that case, Zebra OPTEX was used for the marker pen. As a result, characters with CABOJET-200 ink were disturbed by the rubbing test, and in the marker resistance test, the marker pen was soiled with ink, but this problem did not occur with the ink of this example.

[Example 6]
A dispersible colorant was prepared in the same manner as in Example 1 except that carbon black was changed to Black Pearls L manufactured by CABOT. This carbon black is a product obtained by dry oxidation of carbon black by the furnace method. When the amount of surface oxygen of this dry oxidized carbon black was measured in the same manner as in Example 3, the loss on heating was 5%.

  When ink was prepared by the same method and formulation as in Example 1 and printing was performed using the obtained ink, good character quality and bleed characteristics were realized. However, the character quality and bleed characteristics were inferior to those of the inks of Examples 4 and 5 containing a dispersible color material using wet oxidized carbon. In the case of surface oxidation of carbon black, the dry oxidation method has the advantage of being cheaper than the wet oxidation described above, but the degree of surface oxidation is sufficient compared to the case of wet oxidation. However, since the loss on heating was low, it was confirmed that the character quality and bleedability were inferior to those using wet oxidized carbon black.

[Example 7]
A dispersible colorant was prepared in the same manner as in Example 1 except that instead of carbon black, yellow pigment PY-180 (TONER YELLOW HG) manufactured by Clariant was used. The pigment is a yellow pigment having a benzimidazolone structure and is a very hydrophilic pigment.

  An ink was prepared in the same manner as Example 1 using the dispersible colorant obtained above. Then, a printing test was conducted in the same manner as in Example 1. During the printing test, the yellow ink obtained above was filled in a yellow ink tank of S-700. At the same time, the black ink prepared in Example 4 was injected into the black ink tank of S-700, and a printing test was performed. Both black and yellow showed good color developability. When the boundary between black and yellow color tone was observed, almost no mixed color bleeding occurred, and it was confirmed that particularly good bleeding characteristics could be obtained by combining these inks.

  According to the present invention, by using an ink in which a specific salt is used in combination with a dispersible colorant in a novel form, the ink has an extremely high character quality and good color developability and bleed characteristics. Suitable aqueous inks are provided. In addition, the recorded matter obtained using the ink according to the present invention has excellent properties in terms of scratch resistance and marker resistance despite the use of a water-insoluble colorant. Although the ink according to the present invention uses a dispersible color material, it is excellent in long-term storage stability, and in this respect as well, a water-based ink suitable as an inkjet ink is provided.

It is a schematic diagram which shows the basic structure of the dispersible color material which has fixed the chargeable resin pseudo fine particles by this invention. It is a schematic diagram of the typical process in the manufacturing method of this invention. It is a schematic diagram which shows the refinement | purification of the chargeable resin pseudo fine particles and the adhering process to a color material in the manufacturing method of this invention. It is the schematic diagram which expanded the chargeable resin pseudo fine particle of this invention from the interface side fixed to a coloring material. It is the schematic diagram which expanded the interface which the chargeable resin pseudo fine particles of this invention and the coloring material adhere. It is a schematic diagram of a pigment peeling phenomenon when a hydrophilic group is directly modified on an organic pigment, represented by Patent Document 1. FIG. 6 is a schematic diagram illustrating an aggregation state of a dispersible color material on a recording medium.

Explanation of symbols

1: Color material 1a: Part of color material 2: Charged resin pseudo fine particles 3: Dispersant 4: Monomer 5: Polymerization initiator aqueous solution 6: Dispersible color material 7: Oligomer 8 formed by polymerizing monomers: Precipitate in which oligomer is insolubilized in water 9-1: Hydrophilic monomer unit portion 9-2 in charged resin pseudo fine particle: Hydrophobic monomer unit portion 10 in charged resin pseudo fine particle 10: Binding site 11 with coloring material 11: Interfacial portion 12 of the chargeable resin pseudo fine particles with the colorant 12: hydrophilic group modified directly on the colorant 13: hydrophilic colorant molecule 14: recording medium 15: repulsive force acting between the chargeable resin pseudofine particles

Claims (8)

In a water-based ink containing a colorant and water, the colorant has a coloring material and charged resin pseudo fine particles smaller than the coloring material, and the coloring material and the charged resin pseudo fine particles are fixed. (M1) ₂ SO ₄ , CH ₃ COO (M1), Ph—COO (M1), (M1) NO ₃ , (M1) Cl, (M1) Br , (M1) I, (M1) ₂ SO ₃ and (M1) CO ₃ (wherein M1 represents any one of alkali metal, ammonia or organic ammonium, and Ph represents a phenyl group). An aqueous ink comprising at least one selected salt.   The water-based ink according to claim 1, wherein the salt is contained in an amount of 0.05 to 5 mass% in the ink.   The water-based ink according to claim 1 or 2, wherein the color material constituting the dispersible color material is a color material whose surface is oxidized.   The water-based ink according to claim 3, wherein the color material constituting the dispersible color material is wet-oxidized carbon black.   The water-based ink according to claim 3, wherein the color material constituting the dispersible color material is carbon black that has been dry-oxidized.   The water-based ink according to any one of claims 1 to 5, which is for inkjet recording.   The ink set for inkjet recording which is an aqueous ink of any one of Claims 1-5 in the ink set for inkjet recording which has 2 or more types of aqueous inks. The ink set for inkjet recording according to claim 7, wherein the two or more water-based inks have different color tones and are water-based inks according to claim 1.

Images